Some marine vessel propulsion systems utilize waterjet propulsion. Such devices include a pump, a water inlet or suction port and an exit or discharge port, which generate a waterjet stream that propels the marine vessel. The waterjet stream may be deflected using a “deflector” to provide marine vessel control by redirecting some waterjet stream thrust in a suitable direction and in a suitable amount.
It is sometimes more convenient and efficient to construct a marine vessel propulsion system such that the flow of water through the pump is always in the astern direction, and to have the pump remain engaged in the forward direction (water flow directed astern) while providing other mechanisms for redirecting the water flow to provide the desired maneuvers.
One example of a device that redirects or deflects a waterjet stream is a conventional “reversing bucket,” found on many waterjet propulsion marine vessels. A reversing bucket deflects water, and is hence also referred to herein as a “reversing deflector.” The reversing deflector generally comprises a deflector that is contoured to at least partially reverse a component of the flow direction of the waterjet stream from its original direction to an opposite direction. The reversing deflector is selectively placed in the waterjet stream and acts to generate a backing thrust, or force in the backing direction. A reversing deflector may be partially deployed, placing it only partially in the waterjet stream, to generate a variable amount of backing thrust. By so controlling the reversing deflector and the waterjet stream, an operator of a marine vessel may control the forward and backwards direction and speed of the vessel.
Safe and useful operation of such waterjet propelled marine vessels also requires the ability to steer the vessel from side to side. Systems for steering marine vessels, commonly used in waterjet-propelled vessels, rotate the exit or discharge nozzle of the waterjet stream from one side to another. Such a nozzle is sometimes referred to as a “steering nozzle.” Hydraulic actuators may be used to rotate an articulated steering nozzle so that the aft end of the marine vessel experiences a sideways thrust in addition to any forward or backing force of the waterjet stream. The reaction of the marine vessel to the side-to-side movement of the steering nozzle will depend on the dynamics of the marine vessel design.
Despite the proliferation of the above-mentioned systems, some maneuvers remain difficult to perform in a marine vessel. These include turning the vessel in tight quarters, slowing down or stopping the vessel without forcing the bow down and generally controlling the vessel at slow speeds in a precise manner.